The present invention generally relates to taxi drive systems and more particularly, systems for transmitting torque to wheels of an aircraft.
A typical aircraft may taxi to and from runways with thrust force developed by its engines. A significant amount of fuel may be burned by the engines during a typical aircraft taxi profile before and after each flight. In many cases, the main engines may provide more motive force than is required to complete a successful taxi profile. In that regard, engine-thrust taxiing may be considered inefficient and may contribute to high fuel costs and ground level emissions.
Aircraft designers have sought a more efficient method for propelling an aircraft during taxiing. Electric taxi systems (ETS) have been proposed to provide higher efficiency. An ETS may be implemented by using electrical motors to provide the motive force for aircraft taxiing. While this general ETS concept holds promise for improved efficiency, there are practical application problems that need to be addressed in any successful ETS design. For example, it is desirable that an ETS should be selectively engageable with wheels of the aircraft so that the ETS does not impact normal take-off and landing procedures or aircraft performance. It is also desirable to construct an ETS with compact and lightweight components which may be retrofitted onto existing aircraft and may perform reliably even when exposed to varying environmental conditions that may be encountered by the aircraft at various airports.
The wheel rims of many commercial aircraft are designed to allow a limited amount of deflection during taxiing and turning of the aircraft. For example, during taxiing, the load of the aircraft may cause the wheel to ovalize on each revolution. Moreover, the loads exerted on the wheel may cause deflections of the wheel rim with respect to the axle. For example, weight on the axle during a turn may cause flexure of the wheel rim radially or axially from the drive element as the drive element may not want to flex with the load forces.
Such deflections can be reduced by making aircraft wheels more stiff. But, wheel designs which allow for such deflections have been found to be less likely to experience metal fatigue failures. However, wheel deflections may present difficulties to designers of an ETS. The combination of wheel ovalization and axial deflections caused by wheel side load conditions and axle bending may compromise the structural integrity in the interface between the ETS drive and the wheel. For example, point loading of forces on drive elements may lead to wear issues over time, expediting failure of the connection between the ETS and the wheel
As can be seen, there is a need for a system in which an ETS drive may be reliably coupled to an aircraft wheel to transmit torque to the wheel. More particularly, there is a need for an ETS coupling system in which point loading of drive elements does not produce undesirable wear of the drive elements.